Structural frameworks employing precast structural components are now used extensively in the construction industry. One system that has gained considerable commercial acceptance is described in U.S. Pat. No. 3,429,092 dated Feb. 25, 1969.
In this system steel pipes are cast in the columns to form hollow cores. Superimposed columns are then joined in load transmitting relationship to each other by means of a threaded spindle having oversized nuts threaded thereon, with the ends of the spindle being received in the hollow cores of the columns and the nuts bearing against the exposed ends of the pipes cast in the columns to transmit load from an upper column to a lower column.
Aside from the fact that this provides an indirect stress transfer path, that is, from a column end to a nut, from the nut to the spindle, from the spindle to the lower nut and thence to the lower column, it will be apparent that providing interfitting threaded components, which are used in substantial numbers in a building system of this type, increases the overall cost of construction.
Additionally, although the columns are cast to rigid dimensional specifications, generally the pipes cast into the columns are of an inexpensive grade and inside pipe diameters may vary considerably. Thus, difficulties have been encountered in inserting the threaded spindles into the column cores and while the threaded spindles can be turned down to reduce their external diameter this may require rethreading and the use of different sized nuts, again increasing the cost of construction.
Despite this, it has been felt that a threaded connector was necessary due to the fact that it is desirable to set the columns at fairly precise elevations.